SOAP

To communicate between two parts of the same application, or between two distinct applications, programmers have until now been able to use three proposals that are not easily compatible: COM+, the distributed version of Microsoft's object model, limited in practice to the Windows world; CORBA, the normative specification for a multi-platform, multi-language object bus; and the Enterprise Java Beans (EJB) model, an architecture specification for the construction and execution of Java components proposed by Sun. Irrespective of the contributions of the two, which are outside the scope of this study, few software gateways allow requests from one environment to be easily converted and accepted in another. It is therefore illusory to simply try to make several interconnection software buses ("middleware") cohabit within the same application. As the need is essential, several types of gateway exist.

Microsoft, IBM and others, observing that the incompatibilities and cumbersomeness of these proposals led to the development of solutions based on HTTP requests, introduced SOAP (Simple Object Access Protocol), a very simple protocol for communication between objects, based on the achievements of the Internet. In particular, SOAP uses XML to describe requests and HTTP to transport them, thus avoiding the problems associated with firewall filtering. These two widely-used standards are used instead of any other proprietary schema. To be more precise, SOAP consolidates and makes normative an existing "XML-RPC" proposal. SOAP, submitted to the IETF and adopted by the W3C, fills a gap in the Web.

The aim of this document is to present SOAP's operating principles and give a few examples of its use.